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Abstract

In the early 1990s, when the second 5-year plan for the Human Genome Project-which requested more money than any previous research project in biology-was written, common disorders were presented as the future target of genome research. This was a clever move to ensure continued public support for this endeavor, which had been justified previously by the prospect that it would lead to the diagnosis, prevention, and therapy of severe, but mostly rare, Mendelian disorders. Today, more than 15 years later, after billions of dollars have been spent on genome-wide association studies (GWAS), very few major genetic risk factors for common diseases have been identified, and the enthusiasm for large GWAS is dwindling. At the same time, there is renewed interest for studying single gene disorders, which are now considered by some as a better clue to the understanding of common diseases. While this is probably true, Mendelian disorders are also important in their own right, since they must be far more common than generally thought. As discussed here, various efficient strategies exist for the elucidation of single gene defects, and their systematic application in combination with novel genome partitioning and massive parallel sequencing techniques, will have far-reaching implications for health care.